Some hardware loving Germans have come up with some "neue" details regarding the RV870. The details are said to come from an inside source.
Here's the break down: the GPU is going to be a 40nm part. It's going to have 1/4 (or +%25) more shaders compared to the HD 4870. The theoretical computational horsepower is going up to 1.5 TFLOPS, which is pretty insane (the HD 4870 has about 1 TFLOP.)
I'm not sure if this is a translation error, or so some sort of hardware-freaks kinky pet-name, but the new card appears to have the code-name Lil Dragon. Not sure if this is an internal codename or just something some German writer guy with a job similar to my own just came up with just now to throw me off.
The GPU will be very tiny. The die is supposedly 205 mm˛. Compare this to the RV770 being 256 mm˛, and the GTX 280 being a big 576 mm˛.
DirectX 11 is most certainly going to be there. DX11 is generally accepted to be happening in mid 2009, probably with the first DX11 games coming out in the third quarter of 2009. My prediction is going to be that DX11 will actually bring some significant changes, and will exist, unlike DX10, which came (and will leave) with hardly anyone noticing. (And no, you will not have to upgrade to Windows 7 for DX11 -- it'll be a download for Vista.)
ATI looks like it'll stick with GDDR5 memory, tied to a 512 bit memory interface. The source pins the memory bandwidth at 150-160 GB/s, which seems completely reasonable.
And here is where things get really interesting. The HD 5870 supposedly uses some sort of cooling that ATI hasn't tried before. And thanks in part to the small size of the GPU, the HD 5870 X2 is going not have two seperate GPU's -- instead it will be two RV770 cores stacked on top of each other, sort of like Pentium-D style.
If this is the case, theoretically you could put three HD5870X2 into one motherboard, giving you like six times the power of one of HD5870 -- now that'd be performance. Of course, back in the real world, things don't scale very well after 3 GPU's are CrossFire'd. But who knows, maybe ATI will work some CrossFireX magic up, who knows.
Disclaimer: These are all rumors. All these specs seem sort of reasonable and makes sense, but none of this stuff is confirmed.